This project comprises ongoing studies previously supported extramurally which are being continued in the LCS as well as studies initiated since the PI joined the LCS on February 1, 1987. This work on the development of the cerebral cortex which relies heavily on neuroanatomical techniques focuses on the role of eliminatory events which occur during normal brain development. Much of our effort has concentrated on the transient occipital cortical component of the pyramidal tract which we previously identified. We have recently found that in animals in which the occipital cortex receives an induced aberrant somatosensory input through the lateral geniculate nucleus as a result of neonatal enucleation and rostral cortical lesion, some occipital neurons will maintain a spinal projection. In addition, we have recently identified axonal eliminatory phenomena which occur during the development of the fornix, of the projections of the locus coeruleus, and of the major ascending thalamic afferent systems. Finally, we have continued our studies of the projections extended and maintained by heterotopic cortical transplants made during development. All of our findings in these experiments point to cortical locale as a decisive factor in determining which of the initially extended projections a cortical neuron will maintain.